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--===========================================================================----

--

--  S Y N T H E Z I A B L E    ioport - 2 x 8 bit parallel I/O port

--

--  www.OpenCores.Org - September 2003

--  This core adheres to the GNU public license  

--

-- File name      : ioport.vhd

--

-- Purpose        : dual 8 bit I/O module for System09

--

-- Dependencies   : ieee.Std_Logic_1164

--                  ieee.std_logic_unsigned

--

-- Uses           : None

--

-- Author         : John E. Kent      

--                  dilbert57@opencores.org      

--

--===========================================================================----

--

-- Revision History:

--===========================================================================--

--

-- Version 0.1 - 11 Oct 2002

--   Used a loop counter for data direction & read port signals

-- Version 0.2 - 5 Sept 2003

--   Reduced to 2 x 8 bit ports

-- Version 1.0 - 6 Sept 2003 - John Kent

--   Realeased to open Cores

--   changed Clock Edge

-- Version 1.1 - 25 Feb 2007 - John Kent

--   modified sensitivity lists

--

--===========================================================================

--

library ieee;

  use ieee.std_logic_1164.all;

  use ieee.std_logic_unsigned.all;

entity ioport is

        port (

         clk       : in  std_logic;

    rst       : in  std_logic;

    cs        : in  std_logic;

    rw        : in  std_logic;

    addr      : in  std_logic_vector(1 downto 0);

    data_in   : in  std_logic_vector(7 downto 0);

         data_out  : out std_logic_vector(7 downto 0);

         porta_io  : inout std_logic_vector(7 downto 0);

         portb_io  : inout std_logic_vector(7 downto 0)

         );

end;

architecture rtl of ioport is

signal porta_ddr : std_logic_vector(7 downto 0);

signal portb_ddr : std_logic_vector(7 downto 0);

signal porta_data : std_logic_vector(7 downto 0);

signal portb_data : std_logic_vector(7 downto 0);

begin

--------------------------------

--

-- read I/O port

--

--------------------------------

ioport_read : process( addr,

                     porta_ddr, portb_ddr,

                                                        porta_data, portb_data,

                                                   porta_io, portb_io )

variable count : integer;

begin

      case addr is

             when "00" =>

                    for count in 0 to 7 loop

            if porta_ddr(count) = '1' then

              data_out(count) <= porta_data(count);

            else

              data_out(count) <= porta_io(count);

            end if;

                         end loop;

                  when "01" =>

                    for count in 0 to 7 loop

            if portb_ddr(count) = '1' then

              data_out(count) <= portb_data(count);

            else

              data_out(count) <= portb_io(count);

            end if;

                         end loop;

             when "10" =>

                    data_out <= porta_ddr;

                  when "11" =>

                    data_out <= portb_ddr;

                  when others =>

                    null;

                end case;

end process;

---------------------------------

--

-- Write I/O ports

--

---------------------------------

ioport_write : process( clk, rst, addr, cs, rw, data_in,

                        porta_data, portb_data,

                                                                porta_ddr, portb_ddr )

begin

  if clk'event and clk = '0' then

    if rst = '1' then

      porta_data <= "00000000";

      portb_data <= "00000000";

      porta_ddr <= "00000000";

      portb_ddr <= "00000000";

    elsif cs = '1' and rw = '0' then

      case addr is

             when "00" =>

                    porta_data <= data_in;

                    portb_data <= portb_data;

                    porta_ddr  <= porta_ddr;

                    portb_ddr  <= portb_ddr;

                  when "01" =>

                    porta_data <= porta_data;

                    portb_data <= data_in;

                    porta_ddr  <= porta_ddr;

                    portb_ddr  <= portb_ddr;

                  when "10" =>

                    porta_data <= porta_data;

                    portb_data <= portb_data;

                    porta_ddr  <= data_in;

                    portb_ddr  <= portb_ddr;

                  when "11" =>

                    porta_data <= porta_data;

                    portb_data <= portb_data;

                    porta_ddr  <= porta_ddr;

                    portb_ddr  <= data_in;

                  when others =>

                    null;

                end case;

         else

                    porta_data <= porta_data;

                    portb_data <= portb_data;

                    porta_ddr  <= porta_ddr;

                    portb_ddr  <= portb_ddr;

         end if;

  end if;

end process;

---------------------------------

--

-- direction control port a

--

---------------------------------

porta_direction : process ( porta_data, porta_ddr )

variable count : integer;

begin

  for count in 0 to 7 loop

    if porta_ddr(count) = '1' then

      porta_io(count) <= porta_data(count);

    else

      porta_io(count) <= 'Z';

    end if;

  end loop;

end process;

---------------------------------

--

-- direction control port b

--

---------------------------------

portb_direction : process ( portb_data, portb_ddr )

variable count : integer;

begin

  for count in 0 to 7 loop

    if portb_ddr(count) = '1' then

      portb_io(count) <= portb_data(count);

    else

      portb_io(count) <= 'Z';

    end if;

  end loop;

end process;

---------------------------------

end rtl;